Hitherto, for flame retardation of flammable resins, there have been employed methods of adding chlorine-containing compounds, bromine-containing compounds, antimony trioxide or the like to resins. However, use of these compounds is considered undesirable from the viewpoint of environmental protection and from the aspect of toxicity, and improvement of the method of flame retardation is demanded. As a flame retardation method using no chlorine-containing flame retardants or bromine-containing flame retardants, it is attempted to use phosphorus-based flame retardants.
The mechanism of the flame retardation using the phosphorus-based flame retardants is considered that a film of carbonized layer produced by dehydration of resin and polyphosphoric acid phase formed on the surface of the resin during burning intercepts the supply of heat and oxygen to the resin during burning. This method is particularly effective for resins which readily form the carbonized film, namely, which is readily dehydrated. On the other hand, when resins which can hardly form the carbonized film by the dehydration are flame retarded with phosphorus and phosphorus compounds, the flame retardation must be relied mainly upon the polyphosphoric acid phase film and, hence, the amount of phosphorus and phosphorus compound must be increased. Therefore, in order to flame retard the resins which can hardly form the carbonized film without increasing the amount of phosphorus and phosphorus compound, there occurs an idea to use a flame retardant composition which previously contains a component which acts as a starting material for the carbonized film.
Patent Document 1 proposes a method of using a crosslinked phosphazene compound and a polyphenylene ether resin as a flame retardant for polyalkylene arylate resins. According to this method, satisfactory flame retardance is imparted to polyalkylene arylate resins. However, processability, heat resistance, mechanical properties, dielectric properties of the resins and appearance of molded articles cannot be sufficiently satisfied.
Furthermore, Patent Document 2 proposes a flame retardant composition comprising a low-molecular weight polyphenylene ether resin and a phosphazene compound, and Patent Document 3 proposes a flame retardant composition comprising a low-molecular weight polyphenylene ether resin and a phosphorus compound other than phosphazene, and these flame retardant compositions are effective from the viewpoints of flame retardance and molding processability. However, demands for molding processability, mechanical properties, dielectric properties and heat resistance and reduction in the amount of flame retardants are everlasting and further improvement in these points is desired.
Furthermore, Patent Document 4 proposes a composite flame retardant comprising a metal element-containing compound and an aromatic group-containing phosphazene compound. However, Patent Document 4 does not disclose specific examples of the metal element-containing compounds used therein. Moreover, silicon compounds, magnesium hydroxide and the like used in Patent Document 4 tend to deteriorate the dielectric properties. Therefore, the flame retardant proposed in Patent Document 4 is not preferred in the fields which require dielectric properties, such as electric and electronic uses, and flame retardants which do not cause deterioration of dielectric properties are demanded.
Patent Documents 5-7 disclose resin compositions comprising in combination an aromatic resin, a phosphazene compound and a metal compound. These patent documents do not disclose which compounds are specifically meant by the metal compounds and which metal oxides, metal hydroxides, etc. are specifically included. Furthermore, the metal hydroxides used in Patent Documents 5-7 are not preferred because they tend to deteriorate dielectric properties and mechanical properties. These conventional technologies do not teach the effects to improve and maintain in well-balanced state various properties such as heat resistance, moisture absorption resistance, mechanical properties, dielectric properties, extrudability and low smoke emission in addition to flame retardance. These excellent effects have been obtained for the first time by the present invention as explained hereinafter.
Patent Document 1: WO03/002666
Patent Document 2: PCT/JP03/06581
Patent Document 3: Japanese Patent Application No. 2003-294180
Patent Document 4: JP-A-2001-247870
Patent Document 5: JP-A-2003-342482
Patent Document 6: WO03/046083
Patent Document 7: WO00/00541